The Reagan administration, in its first high-level contacts with Israel, took a reserved position yesterday on Israeli requests for a renewed American initiative in the Middle East peace process and against the upgrading of F15 fighter planes on order for Saudi Arabia.

The Israeli requests were presented by Foreign Minister Yitzhak Shamir in discussions with Secretary of State Alexander M. Haig Jr. and other senior officials. Shamir is the highest ranking Israeli official to visit here since the new administration came of power.

According to sources close to the talks, Shamir's principal push was for immediate and vigorous U.S. diplomatic action to bring about resumption of high-level meetings and substantive progress in the Israeli-Egyptian negotiations on Palestinian autonomy flowing out of the Camp David agreements.

Shamir reportedly argued that it would be dangerous to permit a hiatus in the talks between now and the Israeli election June 30 and that the United States should play a central role in restoring the momentum.

Haig and other leading foreign policy figures in the new administration have shown no eagerness for such a major U.S. push in the autonomy talks before the election, which will determine Israel's leadership for the next few years.

Nor has there been any sign that Egyptian President Anwar Sadat, who has made no secret of his frustration with Israeli Prime Minister Mehachem Begin, is in a hurry to pursue the negotiations during the preelection period.

A working meeting of U.S., Israeli and Egyptian diplomats was held several weeks ago to discuss the autonomy talks, and another such meeting is expected within a few days, according to U.S. sources. But there is little expectation that such contacts will lead to major progress in the talks in the absence of political-level decisions, which often has required strong U.S. initiative.

According to Israeli sources, Shamir was told yesterday that the United States will have to discuss the next steps with Egyptian authorities before giving a further answer. Shamir will have another chance to plead his case when he sees President Reagan early next week.

The other principal question, the supply of extra fuel tanks and bomb racks that would increase the range and effectiveness of the F15s to be supplied to Saudi Arabia, was "discussed at length in a full spirit of consultation" with the Israeli foreign minister, Haig told reporters.

Shamir reiterated public and private Israeli opposition to upgrading the Saudi planes. At the same time, Israeli sources continued to say that Israeli is hoping to avoid a confrontation on the issue with the Reagan administration, which has been moving toward approval of the Saudi request.

The State Department announced that the U.S. ambassador to Saudi Arabia, John C. West, a Democrat and a Carter administration appointee, has been asked to remain at his post "for some weeks" due to the importance of that country.

Informed sources said West may be needed in the immediate future to conduct the Saudi end of discussions on upgrading the F15s, which the Saudis see as a litmus test of their relations with Washington.

West's successor as U.S. ambassador to Saudi Arabia, it was learned, will be Robert G. Neumann, vice chairman of Georgetown's Center for Strategic and International Studies and a senior adviser to Reagan on Middle East affairs during the presidential campaign. Neumann was director of the Reagan transition team at the State Department following the November election.

Selection of a senior figure close to Reagan as ambassdor to Saudi Arabia underscored the importance being placed on relations with the oil sheikdom and the quandary of the Reagan administration in seeking to accommodate both the Saudis and Israelis on the F15.